Centrifugal ball mill



June 21, 1949. E, wuENscH l 2,473,558 I CENTRIFUGAL BALL MILL C. E` WUENSCH CENTRIFUGAL BALL MILL June 2l, 1949.

Filed March 20, 1944 2 Sheets-Sheet 2 /Anw H INVENTOR. Ummm ERB Wvmscfl.

Patented .Pune 2l, 1949 UNITED STATES PATENT OFFICE CENTRIFUGAL BALL MILL Charles Erb Wuensch, Saratoga, Calif. Application March 20, 1944, Serial No. 527,217

12 claims. l

My present invention relates to an improved,

lcontinuously operating ball mill, and more particularly to a combined centrifugal type ball mill and means responsive to the density of the pulp flowing from the mill for regulating the flow of unground material and/or fluid to the mill.

The main object of my invention is to provide a grinding mill of the ball type in which centrifugal action is relied upon to effect the grinding operation in an eifective and highly eflicient manner.

Another object of the invention is to provide a novel type of ball mill in which a fluid is introduced into the mill during the grinding operation for the purpose of carrying away the pulp or fines while the larger unground particles and balls are recirculated within the mill for further grinding.

Another object of the invention is to provide a. combined centrifugally operating ball mill and classifier in which the fines or pulp produced within the mill is classied and continuously withdrawn therefrom in a new and novel manner.

Other objects and advantages of the invention will be in part evident to those skilled in the art and in part pointed out hereinafter in the following description taken in connection with the accompanying drawing, wherein there is shown by way of illustration and not of limitation preferred embodiments of the invention.

In the drawings:

Figure 1 is a side elevation of a preferred embodiment of my invention with parts broken away and in section to show details of construction,

Figure 2 is a partial view showing amodied form of my invention, with parts broken away, and diagrammatically illustrating a system of control for the mill, and

Figure 3 is a fragmentary sectional view taken along line III-III of Figure 2 and showinga detail of construction.

In the mill of my invention resort is had to the use of balls for effecting the ore crushing operation, but, unlike ordinary ball mills, the crushing action of the balls is implemented by agitation due to centrifugal forces imparted theretwby a turntable or rotor-like element disposed in the bottom of an enclosing housing through which a circulation of fluid, such as water, is maintained. 'lnl mill where they will return by gravity to the centrifugal rotor-like element. At the same time, the finely ground particles of the material. due to their reduced mass, will become separated from the unground particles and will be entrained by a counter-current ilow of the uid within the mill. As an additional adjunct, my invention also contemplates the provision of a Weir-like discharge outlet at the top of the mill and through which the slime or pulp resulting from the entrainment of the nely ground particles. will be discharged. This Weir-like discharge outlet, in its preferred form, consists of a cylindrical member that extends downwardly into the pulp within the mill and upwardly a distance suicient to provide a quiescent column of flowing pulp, the specific gravity or density of which is measured at its ends and is relied upon to control the operation of the mill by regulating the feed ofthe ore or material to be ground and/or the iluid which, as suggested above, is circulated through the mill.

Upon referring to Figure 1 of the drawings it will be seen that the enclosing housing of the mill, designated generally by the numeral Ill, is of substantially elliptical form in cross-section and is supported in an elevated position upon four` columns Il that are carried by a base I2. The housing I'D is here shown as composed of a sheet metal shell, but it will be understood that this housing may be constructed of cast steel sections.

f It has an upper portion i3 that is secured in cooperating relation with a lower portion Il. The

l lower portion Il of the housing lll is recessed, as at l5, to provide an accommodating space for a order to prevent a swirling action within the mill,

turn-table or rotor-like elementV I6 which. when in operation, will centrifugally agitate a plurality of balls I1 and also the material to be ground.

Surrounding the perimeter of the rotor-like element IB there is a replaceable wear resisting ring Il over which the material 4and the balls move. Extending downwardly from the recessed portion i5 of the housing I0 there is a cylindrical portion I9 that surrounds a vertically extending pedestal 20 within which a vertical shalt 2|, that carries the rotor-like element l0 is journaled. The pedestal 20 extends upwardly into the cylindrical portion i9 of the housing In, and in conjunction therewith it provides an annular well into which a skirt 22 carried by the rotor-,like element IB extends. The annular well so formed supports a pool of mercury or other sealing uid 23 intoA which the lower edge of the skirt 22 is immersed to thus provide a fluid-tight seal between the interior of the enclosing housing l0 and the rotating shaft 2l upon which the rotor-like element I6 3 is mounted. The shaft 2| is supported within the pedestal 23 by means of thrust supporting roller bearings 24, and at its lower end it carries a beveled gear 25 that is engaged by a beveled pinion 26 upon the end of a driving shaft 21 that may be connected to any suitable prime mover unit. Communicating with the interior of the cylindrical portion I9 of Ithe housing I0 there is a pipe connection or conduit 28 through which fluid may be introduced in a downwardly direction into the interior of the housing I when the 'mill is in operation. As a means for indicating the level of the mercury or sealing fluid 23, the cylindrical portion I9 carries a sight glass 29 through which the level of the sealing fluid may be ob- Wserved. At this point it will be noted that the material being ground by the rotor-like'element I6. As here shown, the upper portion I3 of the housing I8 carries a plurality of upwardly and diagonally extending cylindrical columns or sleeve-like brackets 3| in each of which there is slidably mounted a plow rod 32 that preferably terminates at a point immediately above the replaceable wear resisting ring I8. In the drawings, four of these plow rods 32 are shown, but it will be understood that any desired number of these rods may be provided. It will also be understood that the inclination of these rods may vary between wide limits, depending upon the nature of th'e material to be ground, the size of the grinding balls and/or the operating speed of the rotorlike element I6. The function of these plow rods 32 is first to retard and prevent, to a large degree, any horizontal swirling action of the centrifugally flung balls and material within the mill which might reduce the grinding action of the balls. These plow rods 32 also serve to establish a back pressure within the agitated mass of material and balls which will greatly facilitate the grinding action, and because of their inclined disposition, they will impart an upward swirling motion to the moving mass which will recycle the larger particles and the balls back to the centrifugal rotor-like element I6, and as a final function theyalso facilitate the separation of the finely ground particles from the agitated mass so that the flnes will flow from the mill as a pulp or slime, as will now be described.

For the purpose of removing lthe flnelyground particles of the material from the mill in the form of a pulp or slime, the upper portion I3 of the enclosing housing I3 is shown as having a relatively large central opening through which a cylindrical conduit forming pipe 33 of relatively large diameter is extended. At its upper end this cylindrical conduit forming pipe 33 is turned over and forms a substantially level weir-like discharge outlet over which the pulp or slime will ow into a launder 34 that is disposed therearound. The launder 34 has a conduit 35 into which the pulp or slime is collected and directed away from the mill. The lower end of the cylindrical conduit forming pipe 33 is perforated, as at 36, and extends downwardly into the interior of the enclosing housing I0 below the level of the pulp therein so that it will form a substantially quiescent zone of pulp at the outlet of the mill. Positioned centrally above the rotor-like element I6 and extending downwardly into the enclosing '4 housing I0 and terminating beyond the lower end of the cylindrical conduit forming pipe 33 there is a second pipe or conduit 31 through which the ore or other material to be ground is introduced into the mill. In this way the ore or material to be ground will be fed directly to the rotor-like element I6 and effectively set in motion and mixed with the grinding balls I1 while, 'at the same time, the uid that is introduced into the interior of the housing I0 through the conduit 28 will be caused to whirl upwardly along the sides of the mill by the diffusing action of the rotor-like element and thus effectively flush the slimes from the material as lt is being ground.

With the above described arrangement it will be seen that as the material is'ground, the finer particles will accumulate at the top of the mill in the form of a pulp or slime. This pulp or slime will then enter the cylindrical outlet conduit forming pipe 33 through its lower open end and the perforations 36 and thus be discharged from the mill. Because of the length and downwardly extending nature of the conduit forming pipe 33,

there will be formed a zone of pulp or slime which will be more or less free of turbulence and which will slowly flow toward the upper or discharge end of this conduit. As a result, there will be provided a quiescent zone of pulp, the density of which may be measured without any error being introduced due to turbulence. such as exists within the grinding zone of the mill. In this figure of the drawings two density responsive gauges or devices 38 and 39 are shown as positioned so as to be submerged at different predetermined levels Within the pulp in this quiescent zone. These devices 38 and 39. together with associated density measuring means, may take many forms. One such device and associated means is illustrated in my copending application entitled Density responsive indicating and control device, Serial No. 579,117, led February 2, 1945. These particular devices 38 and 39 have a pressure responsive diaphragm that is adapted to operate or flex and actuate a circuit controlling switch (not shown) which will open and/or close an electrical circuit 40 or 4I whenever an unbalanced condition exists between the pressure exerted by the head of pulp within the conduit forming pipe 33 and a column of liquid held at the other side of the respective diaphragms by tubular supporting pipes 42 and 43. As will more clearly appear hereinafter, the density gauge 38 is placed near the top of the quiescent depth of pulp and is adapted to automatically control the density of the outowing ground material by regulating the amount of water introduced into the bottom of the mill, and the density responsive gauge or device 39, which is located at a lower level in the discharge conduit 33, operates to regulate the feed of unground material to the mill so as to maintain a predetermined density of pulp. At the ysame time this latter density responsive device 39 will operate to prevent an overloading of the mill. It should also be here pointed out that when the mill is in operation, the weight of the pulp within the mill will offset the mercury or sealing fluid 23 about the rotor supporting pedestal 20. This will uncover y .the enclosing housing III. At their upper ends each of the shafts 41 carry a worm gear 50 that is engaged by a worm 5I which is adapted to be turned by a crank 52. Like the plow rods 32, it is contemplated that the mill will carry a plurality of these paddle or rudder-like deiiectors 46 at equally spaced points around the circumference of the mill. It is contemplated that at least four of these paddles will be required and that a greater number may be desirable for some grinding operations. With this arrangement it will be seen that the angle of thedefiectors 46 may be individually adjusted to any desired degree by a turning of the cranks 52. These defiectors 46 may also be positioned so as to cause substantially no deflection of the ground material and balls if desired. As is more clearly shown in Figure 3 of .the drawings, the deflectors 46 are disposed in trailing relation with their supporting shafts, as is determined by the rotation of the centrifugal rotor-like element I6. These defiectors 46 are also here shown as provided with a wear resisting surface or plate 53 which may be extended out and around the hub portion into which the shaft 41 is keyed.

As is diagrammatically shown in Figure 2 of the drawings, the density responsive gauge or device 38 is adapted to close a normally open circuit controlling switch 54 that is connected in series with an electromagnet 55 that will operate to open a valve 56 through which the iiuid pipe connec- L tion or conduit 28 is connected to a source of supply, and the density responsive gauge or device 39 is shown as adapted to open a normally closed switch 51 that is connected in series with an electromagnet 58 which will operate when energized to open a gate -68 that is interposed in a chute BIJ through which the material to be ground is introduced to the mill from a suitable hopper or other source of supply. In this diagrammatic illustration the switches are shown and described as connected directly in the operating circuits of the electromagnets 55 and 58, but it will be understood that these switches may be connected and used to merely close an auxiliary or control circuit for electromagnetic contactors orswitches that may be better adapted to carry the current required for the operation of the electromagnets 55 and 58. As here shown, the switch 54 associated with the density responsive device 38 is connected to a negative power line conductor 6I by means of a conductor 62, and at its other side it is connected to one terminal of the electromagnet 55 through a conductor 63,A the other side of the electromagnet 55 beingconnected to a positive power line conductor 64 by means of a conductor 65. Likewise, the switch 51 associated with the density responsive device 39 is connected at one side to the negative power line conductor 6I through the conductor 62, and at its other side it is connected through a conductor 66 to one terminal of the electromagnet 58, while the other terminal of the electromagnet 58 is connected to the positive power line conductor 64 through a conductor 61. With this arrangement it will be seen that when the pressure exerted upon the diaphragm of the density responsive device 36 reaches a predetermined high value, the switch 54 will be closed. This will-energize the electromagnet and the valve 56 will be opened to admit a flow of uid through the pipe connection or conduit 28 to the interior of the mili and as a result, the contents of the mill will be diluted and thus the specific gravity or density of the pulp will be lowered. Then when the density reaches a predetermined lower value, the switch 54 will again open and permit the valve 56 to close. In like manner, when the density of the pulp reaches a predetermined lower value, as will be determined by the density responsive device or gauge 39, the switch 51 will close and cause the electromagnet 58 to be energized. This will open the gate 59 in the conduit 60 and permit unground material to flow into the mill. Then as soon as the density of the pulp in the quiescent zone adjacent the density responsive device 39 reaches a predetermined higher value, the switch 51 will again open and disconnect the electromagnet 58 from the power supply conductors 6I and 64 and thus permit the gate 59 to close and stop the flow of unground material to the' mill.

It will be noted in the above description on the operation of the density responsive gauges or devices 38 and 39 that they each operate in response to a predetermined pressure and it should, therefore, be explained that each of the devices 38 and 39 are calibrated or adjusted for operation within different ranges of density by the provision of different heads of counter-balancing liquid of known specic gravity at their inner sides, and in this way they are each made responsive to pulp densities at diierent levels in the pulp. As for example, the density responsive device 38 will respond and operate the switch 54 in a lower pulp density range than will the pressure responsive device 39, and in this way the density of the pulp at the different levels of the pressure responsive devices 38 and 39 will be independently relied upon to respectively control the ow of fluid to the mill through the valve 56 and the amount of aggregate introduced to the mill through the i structed and controlled in accordance with my invention will be readily understood from the above description and it should, therefore, only be necessary to add that Aafter the mill has been charged with the proper number of balls, and the rotor-like element I6 is in rotation with the mill full of water or other iluid, the aggregate may be fed thereto. Then, due to the centrifugal action of the rotor-like element I6, the aggregate fed to the mill and the balls I1 will be thrown outwardly by centrifugal forceat a tangent to the perimeter of the rotor-like element I6 and will strike the plow rods 32 or the deilectors 46 and be redirected to the center of the mill where the heavier particles will settle by gravity upon'the rotor-like element I6 for further grinding. At the same time, `due to their lighter mass, the nes or ner particles of the ground material will become entrained in the counter-current flow of iiuid within the mill and be discharged therefrom through the wear-like discharge outlet conduit 33 where it will be collected by the launder 34 and directed to another point for further treatment. f In th'is action the plow rods 32 or deectors 46 will perform two other important functions; first, they will retard or prevent any swirling movement of the aggregate and balls within the enclosing housing III as the aggregate is beingground and anatre thus build up a strata oi' slow moving material which will form what might be termed a slow moving protective lining within the mill: and second, the plow rods 32 or deiiectors 4t will set up a back pressure within the agitated mass of material within the mill which will greatly facilitate the grinding action of the balls.

Now, if it is assumed vthat the mill is in operation and that pulp of a predetermined density is flowing over the Weir-like discharge end of the conduit 33. it will be seen that should the density of the pulp increase beyond a predetermined value, the density responsive device 38 will operate to close the control circuit of the electromagnet 55 and thus open the valve 55 and permit the introduction of additional pulp entraining fluid to the'mill. This will dilute the contents of the mill and after a sufficient amount of fluid has been introduced into the mill, the density of pulp being discharged through the outlet conduit 33 will be reduced, and when its density `is thus reduced to a predetermined point, the circuit controlling switch l will be again permitted to open by a reverse action of the density responsive device 38. In the same manner it will be noted that when the density o f the pulp flowing through the discharge outlet conduit 33 reaches a value below that at which the density responsive device 39 is calibrated, the circuit controlling switch 51 will be caused to close and thus energize the electromagnet 58 of the aggregate flow controlling gate 59 and thus cause the mill to be charged with an additional amount of the material to be ground. This charging of the mill will continue until the density of the pulp within the mill has been raised to a value which will operate the density responsive device 39 and again open the switch 51. In this way it will be seen that the flow of the pulp from the mill will be automatically regulated between two values of density and, as a result, it will be possibleto operate the mill in a substantially continuous manner with a substantially uniform density of .pulp flowing therefrom.

While I have, for the sake of clearness and in order to disclose the invention so that the same can be readily understood, described and illustrated specific devices and arrangements, I desire to have it understood that the invention is not limited to the particular forms disclosed, but may be embodied in other ways that will suggest themselves to persons skilled in the art. For example, it will be understood that while I have described the switches 54 and 51 respectively as of normally open and normally closed types, these switches may-be operated in a reverse order. is also contemplated that the control of the valve 56 and the gate 59 may be effected by pneumatic or hydraulic means and that photoelectric density control means may be substituted for the hydrostatic density responsive means 38 and 39 as here illustrated. It is believed that this invention is new and it is desired to claim it so that all such changes as come within the scope of the appended claims are to be considered as part of this invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In an ore grinding mill, the combination of a substantially closed housing, means for introducing a material to be ground in a downwardly direction through the top of said housing, means for admitting a counter-current flow of fluid upwardly into the lower part of said housing, a centrifugally operating grinding means located at the lower part of said housing adapted to agitate and throw the material being ground therefrom by centrifugal force, detlector means above said grinding means and within said housing against which the material acted upon by said centrifugal grinding means will impinge, whereby the heavier particles of the material will be returned by gravity to said centrifugal grinding means and the finer particles will be entrained in suspension by the counter-current flow of fluid within the mill, a discharge conduit at the upper part of said housing through which the ground material entrained by the introduced fluid may ow. and density responsive means positioned within said discharge conduit for controlling the admission of new material and fluid into said housing as determined by variations in the density of the entrained material flowing from the mill through said discharge conduit.

2. In a grinding mill, the combination of a substant lly closed housing, means for introducing solid material to be ground in a downwardly direction at the upper part of said housing, means for admitting a flow of fines entrain-v ing liquid in an upwardly direction into the lower part of said housing, a centrifugally operating solid material grinding means located between the points of entry of said solid material and said liquids into said housing, a stationary means within said housing against which the material acted upon by said centrifugally operating grinding means will impinge, whereby the heavier particles will be deflected and returned to said centrifugally operating grinding means by gravity while the finer particles are retained in suspension by the liquid flowing in countercurrent within the mill. a vertically disposed discharge conduit at the upper part of said housing through which the ground material entrained by the introduced liquid may flow, a high density responsive means located at the outlet end of said discharge conduit, a low density responsive means located in said discharge conduit below said high density responsive means, and feed controlling means associated with said high and low density responsive means for respectively controlling the introduction of liquid and solid material into said housing as determined by variations in the density of the entrained ground material flowing from the mill through said discharge conduit.

3. In an ore grinding mill, the combination of a substantially closed housing, means for introducing a material to be Vground downwardly through the top of said housing, means for admitting a ilow of iluid upwardly into the lower part of said housing, a vertically disposed centrifugally operating rotor located between the top and lower part of said housing adapted to receive the introduced material to be ground and throw it outwardly by centrifugal force, deflector means within said housing adapted to redirect the centrifugally thrown heavier particles back to said rotor while the finer particles are retained in suspension by the fluid within the mill, a vertically and centrally disposed discharge conduit at the upper vpart of said housing through which the ground material together with the introduced fluid may flow from the mill as pulp in a counter-current direction, a high density responsivemeans submerged in said pulp at the upper end of said discharge conduit, a low density responsive means submerged in said pulp below said high density responsive means, and feed regulating means controlled by said high and low 9 density responsive means `for respectively regulating the introduction of uid and the material to be ground into said housing as determined by variations in the density oi the pulp ilowing from the mill through said discharge conduit.

4. In a grinding mill, the combination of a vertically disposed bowl-like enclosing housing having a central recess at its bottom, a pan-like rotor element disposed in the central recess at the bottom of said housing and operating about a vertical axis, means at the top of said housing through which the material to be ground is directed down- -wardly to the center of said pan-like rotor element, a conduit connected to said housing through which a flow of liquid'may be directed into said recess and upwardly around said panlike rotor element and into the interior of said housing, means for driving said pan-like rotor at a relatively high speed whereby the introduced material will be thrown upwardly therefrom by centrifugal force, stationary means within said housing'for redirecting the centrifugally thrown larger unground particles of the material backto said rotor element, a Weir-like discharge outlet disposed centrally at the top of said housing over which the iinely ground material entrained byl the introduced liquid may ilow as pulp, a pulp density responsive means submerged in the liquid entrained material approaching said weir-like discharge outlet, and means controlled by said pulp density responsive means for regulating the introduction of new material at the top of said housing and liquid to the recess in said housing, whereby the mill may be regulated to produce a substantially continuous flow of uniformly ground material through said Weir-like discharge outlet.

5. In an ore grinding mill, the combinationgof a u vertically extending housing, a centrifugally operating ore grinding and agitating means disposed at the bottom of said housing, means for feeding material to be ground downwardly to said grinding and agitating means at the bottom of the housing, a vertically disposed conduit extending downwardly and centrally into said housing and forming a Weir-like discharge outlet from the interior of said housing, a launder associated with said weirlike discharge outlet for collecting the f pulp as it is discharged thereover, means at the bottom of said housing for introducing an upward ow of fluid to the interior of said housing, whereby the iines produced by the action of said grinding and agitating means will be entrained by said fluid and continuously discharged as a pulp from the mill by a counter-current ow of said uid, and means responsive to changes in the density of said pulp owing to said Weir-like discharge outlet for regulating the feed of new material at the top of said housing and the ilow of fluid at the bottom of said housing.

6. In an ore grinding mill, the combination of a vertically extending housing, a centrifugally operating ore grinding and agitating means disposed at the bottom of said housing, means for feeding material to be ground in a downwardly direction to said grinding and agitating means at the bottom of the housing, a concentric vertically disposed conduit extending downwardly into said housing and forming a Weir-like discharge outlet from the interior of said housing, a launder associated with said Weir-like discharge outlet for collecting the pulp as it is discharged thereover, means for introducing a ilow of uid upwardly into the interior of said housing, whereby the fines produced by the action of said grinding and agitating means will be entrained by a counter-current ilow of said fluid and discharged as a pulp from the mill, and means responsive to changes in the density of the pulp owing to said launder for regulating the feedfof material to be ground and the ow of fluid to said housing, whereby the density of the pulp flowing from the mill may be maintained at a substantially constant value.

'7. In an ore grinding mill, the combination of a vertically extending housing, a centrifugally operating ore grinding and agitating means disposed at the bottom of said housing, means for feeding material to be ground in a downwardly direction to said grinding and agitating means at the bottom of the housing, a vertically. disposed conduit extending downwardly into said housing and forming a Weir-like discharge outlet from the interior of said housing, a launder associated with said Weir-like discharge outletfor collecting the pulp as it is discharged thereover, means for introducing a ilow of uid upwardly into the interior of said housing, whereby the nes produced by the action of said grinding and agitating means will be entrained by a counter-current flow of said fluid and discharged into said launder as a pulp from the mill, and means operating between two limits of value responsive to changes in the density of said pulp for regulating the ilow of fluid and the feedof new material to said i grinding and agitating means, whereby the density of the pulp discharged into said launder may be maintained at a substantially constant value.

8. In a ball mill of the character described,l

the combination of an enclosing housing, a centrifugally acting bowl-like rotor mounted for rotation about a vertical axis within said housing adapted when in rotation to centrifugally agitato a plurality of ore reducing balls, means for feed-l ing unground material to said bowl-like rotor,"

ing action of said balls will be entrained by saidfluid and separated from the heavier particles as a pulp, a verticallyI disposed conduit extending downwardly into said housing and having a weirlike discharge outlet at its upper end, whereby the larger particles will be separated from said pulp and returned to said bowl-like rotor as the pulp is discharged over the Weir-like discharge and said fines entraining liquid into said housing,

a plurality of ore reducing balls adapted to be agitated and thrown upwardly from said rotor element and into said housing, a plurality of inclined defiector rods within said housing against which said balls and the ore acted upon and thrown by said centrifugally operating rotor element will impinge, whereby said balls and the coarser particles of said ore will be returned to said centrifugally operating rotor element by' 11 gravity while the reduced! ore particles will be retained in suspension by the nnes entraining liquid as it iiows in a counter current direction through the 'mill, and a vertically disposed discharge conduit at the upper part of said housing through which the ground ore together with the introduced liquid may now from the mill.

10. In an ore grinding mill, the combination lof a vertically disposed bowl-like enclosing housing, an inverted cone-like rotor element ot smaller diameter disposed centrally at the bottom oi saidl` housing and operating about a vertical axis, means at the top oi.' said housing through which ore to be ground is ied in a downwardly direction to said rotor element, a conduit communicating with the interior of said housing below said rotor element through which a supply oi' ilnes entraining liquid may be introduced in an upwardly direction about the rim of said rotor element and into said housing, means for driving said rotor element at a relatively high speed,

whereby the introduced ore will be agitated and thrown from said rotor element by centrifugal force, stationary deilector means disposed at spaced points around the interior of said housing and outwardly from the rim of said rotor element for redirecting the larger particles of the thrown ore back to said rotor element, and a weirlike discharge outlet at the top oi.' said housing over which the inely ground ore entrained by the counter current ilow of liquid will be discharged from the top of the mill as pulp. j

11. In an ore grinding mill, the combination of a substantially closed housing, means for downwardly introducing a dry material to be ground into the upper part of said housing, means for admitting a counter current ilow of liquid up-v wardly into the lower part of said housing, a centrifugally operating grinding means located in the lower part oi said housing operable about a vertical axis and adapted to agitata and throw the material being ground outwardly therefrom, a, vertically extending discharge conduit disposed centrally with respect to said grinding means and extending into the upper part oi said housing through which the introduced liquid together with entrained ground material may'ilow at a substantially constant rate, and independently operating high density and low density responsive means positioned at different levels within said discharge conduit for respectively controlling the admission oi' liquid and new -dry material into said housing asy determined by variations at entrained-ground material flowing from the mill through said discharge conduit.

12.In a grinding mill, the combination oi a, vertically disposed bowl-like enclosing housing, an inverted cone-like rotor element disposed at the bottom oi said housing and operating about a vertical axis, means at the top of said housing through which material to be ground is fed in a downwardly direction to said rotor element.' a conduit communicating with the interior of said housing below said rotor element through which a supply oi nnes entraining liquid may be introduced in an upwardly direction about the rim oi said rotor element and'into the mill, means for driving said rotor element at a relatively high speed whereby the introduced material will be thrown from said rotor element by centrifugal force, deilector means disposed outwardly from the rim of said rotor element for redirecting the larger particles of the thrown material back to said rotor element, a Weir-like discharge outlet at the top of said housing over which the nely ground material entrained by the introduced counter current flow of liquid will be discharged as pulp, a high and low pulp density sensitive means disposed Within said Weir-like discharge outlet adapted to respond to changes in the density of the pulp ilowing from the mill, and means controlled by said pulp density sensitive means for regulating the introduction of material at the top of the mill and the introduction of liquid at the bottom of the mill when in operation, whereby a substantially continuous operation of the mill may be maintained.

CHARLES ERB WUENSCH.

REFERENCES CITED The following referenloes are of record in the ille of this patent:

UNITED STATES PATENTS Number 

